What does a circular traffic sign with a red border, white background, black digits, and two horizontal inward-pointing triangles (e.g., '2.5m') indicate?

1. Restriction on Clearance Width: prohibits vehicles whose total loaded width exceeds 2.5 meters from passing
2. Restriction on Clearance Height: prohibits vehicles taller than 2.5 meters
3. Lane Width Advisory: indicates the travel lane is exactly 2.5 meters wide
4. Tire Tread Depth Limit: mandates tire tread width exceeding 2.5 cm